A belt retractor with the aforementioned features is described in EP 1 860 002 A1. In such a belt retractor provided with a belt-webbing-sensitive activation mechanism there can arise the problem, for example, when the belt shaft rotates with such rotational speed in the retracting direction after the seat belt is removed that the belt shaft springs back due to the inertia in the extending direction as a result of the stop of the rotating motion effective at the end of the belt webbing retraction. As a result of the rotation in the direction of belt webbing extension of the belt shaft caused thereby, the belt-webbing-sensitive control system is activated also with a relatively minor angular acceleration, that is, the inertial mass is pivoted into its engaged position with the fixed gearing. The same can occur if the belt webbing retraction is interrupted by a sudden deceleration of the vehicle. This behavior of the belt retractor can have the result that the belt retractor must first be unlocked for further use by pulling on the belt webbing, in order to unlock the control system and subsequently freely pull out the belt. Another problem occurs when the webbing-sensitive control system responds to small vibrations when the seatbelt is unlatched, giving rise to on it desirable rattle noise generation.
In the generic belt retractor described in EP 1 860 002 A1 it is proposed to eliminate this problem by the arrangement of a frictionally engaging torsion spring thus positioned relative to the control plate on a bearing surface for the belt shaft and/or the control plate, with said spring having an Ω shape with a central bearing area provided with radius and spring legs projecting laterally therefrom in opposite directions and extending at an angle of 180 degrees from each other. The one spring leg coacts at the same time with one end of the inertial mass, while the other spring leg is in contact with an actuator that rises up from the plane of the control plate. The frictionally engaged rotation of the torsion spring on its bearing surface that goes along with the different operating states of the belt retractor is produced, on the one hand, by means of the inertial torque of the torsion spring and the inertial torque acting on it and, on the other hand, by means of the interaction with the inertia-controlled motion of the inertial mass. This can lead in a disadvantageous way to control problems in the interactions of the torsion spring with the inertial mass.
It is therefore an object of the invention to further develop a self-locking belt retractor with the generic features in such a way that its operating sequence is improved.